Internal-combustion engines – Valve – Reciprocating valve
Reexamination Certificate
2002-11-19
2004-09-28
Argenbright, Tony M. (Department: 3747)
Internal-combustion engines
Valve
Reciprocating valve
C123S090410
Reexamination Certificate
active
06796281
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an internal combustion engine with a valve train having rocker arms which are spherically supported at proximal end portions thereof and abut with engine valves at operating portions thereof and camshafts disposed above the rocker arms.
2. Description of the Related Art
Conventionally, JP-A-2000-161025 discloses an internal combustion engine with a valve train of this kind. In this internal combustion engine, the valve train comprises rocker arms which abut with valve stems at one end and which are spherically supported at the other end thereof by pivot ends fitted in mount holes in a cylinder head and camshafts disposed above the rocker arms. Cams rotating together with the camshaft are brought into sliding contact with rollers which are rotatably supported at central portions of the rocker arms and oscillate the rocker arms about the other end thereof which acts as an oscillating fulcrum, so as to operate valves to open and close.
Incidentally, in the related art, in assembling the rocker arms and the camshaft to the cylinder head, firstly, the rocker arms are assembled to the cylinder head such that one ends thereof are abutted with the valves slidably held in the cylinder head and the other ends thereof are supported on the pivot ends fitted in the mount holes in the cylinder head. Then the camshaft is lowered toward the rocker arms which are already assembled to the cylinder head, from above the rocker arms so assembled and is then assembled to the cylinder head in such a manner that the cams come into contact with the rollers of the rocker arms. However, since they are spherically supported at the other end thereof, the rocker arms tend to tilt in the axial direction of the camshaft. Then, when attempting to assemble the camshaft to the cylinder head in a state where the rocker arms tilt at an angle larger than an angle through which the rocker arms so tilting can be corrected through the contact with the cams assembled to the cylinder head or in a state where the rocker arms are fallen, there may occur a risk that the rocker arms come off or the surfaces of the cams which are formed of a material having a lower hardness than that of the abutment portions of the rocker arms with the cams are damaged through the contact with the abutment portions.
Due to this, when assembling camshafts, it is necessary to secure a state where the rocker arms occupy preset positions or positions at which the rocker arms do not tilt as resulting when the cams are in abutment with the rocker arms or a state where while the rocker arms slightly tilt, the tilt can be corrected through the abutment with the cams so that the rocker arms can occupy the preset positions. Therefore, a tremendously long time has been needed for assembling the camshafts.
To cope with this problem, it has been desired to provide in an internal combustion engine with a valve train having such rocker arms fall-preventive unit for preventing the fall of the rocker arms when the camshafts are assembled to thereby improve the assembling properties of the camshafts and to make the fall-preventive unit flexible in application depending upon layouts of the rocker arms relative to peripheral components.
In addition, conventionally, a camshaft holder is disclosed in JP-A-6-299807 as this type of integral cam holder for an internal combustion engine. In this camshaft holder (corresponding to the cam holder), crossbars for connecting both longitudinal side walls of the camshaft holder are integrally formed at positions corresponding to journal portions of an intake camshaft and an exhaust camshaft, respectively. An intake-side cam journal portion and an exhaust-side cam journal portion are formed on an upper surface of each of the crossbars. Thus, the camshaft holder is given a ladder frame construction, thereby increasing the rigidity thereof. Then, cam journal portions are formed on a lower surface of a cam cap which rides on an upper surface of the camshaft holder at positions corresponding, respectively, to the intake-side and exhaust-side cam journal portions of the crossbar. The cam caps are then bolted to a cylinder head together with the camshaft holder, whereby the camshafts are pivotally supported therebetween.
In general, it is preferable to increase the rigidity of the cam holder in order to secure stable valve train operations over the full operating range of the internal combustion engine. In this respect, according to the related art, since the cam cap to which the intake-side cam journal portion and the exhaust-side cam journal portion are connected is fastened to the crossbar, it is considered that the rigidity of the camshaft holder is increased further by the cam caps so constructed. However, in a case where a cam cap on which only an intake-side cam journal portion is formed and a cam cap on which only an exhaust-side cam journal portion is formed are used as a cam cap such that the separate cam caps are fastened to the crossbar, it is difficult to increase further the rigidity of the camshaft holder by the cam caps so constructed.
SUMMARY OF THE INVENTION
The invention was made in view of these situations, and a first object of the invention is to prevent the fall of rocker arms which are supported on spherical surfaces in an axial direction of camshafts so as to facilitate the assembly of the camshafts from above the rocker arms to thereby improve the assembling properties of an internal combustion engine with a valve train. Further, a second object of the invention is to provide an integral cam holder in which bearing portions provided adjacent to each other in an axial direction of a camshaft and primary and secondary longitudinal frames for connecting the bearing portions to each other are formed integrally, the rigidity of the integral cam holder being increased without depending upon the form of camshaft supporting members which are connected to the cam holder for rotatably supporting the camshaft.
According to a first aspect of the invention, there is provided an internal combustion engine with a valve train, comprising:
a rocker arm having a proximal portion which is spherically supported by an oscillating support member and an operating portion abutting with an engine valve;
a camshaft having a cam adapted to be brought into sliding contact with the rocker arm and disposed above the rocker arm, wherein the engine valve is operated to open and close by the rocker arm which is oscillated by the cam which rotates together with the camshaft; and
fall-preventive units provided in such a manner as to face both sides of the rocker arm in an axial direction of the camshaft, for preventing the fall of the rocker arm in the axial direction through the contact with the rocker arm.
According to the construction, even in case the rocker arm which is supported on the spherical surface tries to fall in either of the axial directions, the rocker arm comes into contact with either of the fall-preventive units which are provided to face the sides of the rocker arm, whereby the fall of the rocker arm can be prevented. Consequently, according to the first aspect of the invention, the following advantage can be provided. Namely, even if the rocker arm which is supported on the spherical surface tries to fall in either of the axial directions, since the fall-preventive units are provided to face the sides of the rocker arm, the rocker arm comes into contact with either of the fall-preventive units, whereby the fall of the rocker arm can be prevented. Therefore, since there is no risk that the rocker arm falls or comes off when the camshaft is assembled, the assembly of the camshaft which is disposed above the rocker arm can be facilitated, and moreover, there is no risk that cam surface of the cam is damaged by the rocker arm. As a result, a time required for assembling the camshaft can be reduced to thereby improve the assembling properties of the internal combustion engine with such a valve train.
Further, according to a second aspec
Arai Hidemi
Asari Masaru
Hara Ikuro
Mamiya Hiroyuki
Shimoyama Kazuaki
Ali Hyder
Arent & Fox PLLC
Argenbright Tony M.
Honda Giken Kogyo Kabushiki Kaisha
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